Paraphthaloyl chloride (TPC) is a white solid or a colorless acicular crystal, mainly used as a polymeric monomer of poly-p-phenylene terephthamide (p-aromatic polyamide fiber, 1414 or PPTA for short) and polysulfonamide. In addition, the TPC has a certain application in aspects of a modifier for a superpolymer, intermediates of pesticide and medical industries and the like, and prospect of development and application is extensive.
Development of the TPC in China mainly depends on development of aramid 1414, because a purity requirement to a TPC product is very high in production of the aramid, it is to be satisfied that purity is greater than 99.9%, and mono acyl chloride (TMC) is smaller than 600 ppm, Otherwise, a molecular weight, a color, a mechanical property and the like of a high-performance fiber product may be seriously affected.
There are many industrialized preparation technologies for the TPC, one of existing main technology routes is to use paraxylene as a raw material, and the other is to use terephthalic acid (TPA) as the raw material. Herein the paraxylene is used as the raw material, the paraxylene firstly reacts with a chlorine gas to prepare p-hexachloro-xylene, and the p-hexachloro-xylene is hydrolyzed or reacts with the corresponding TPA, so the TPC is obtained. Using the TPA as the raw material phosgene or thionyl chloride direct chlorination method is a technology route generally adopted by existing domestic production factories for preparing the paraphthaloyl chloride.
In CN1054062A, a technology for synthesizing TPC by TPA, PCl3 and Cl2 as raw materials is disclosed, in which a reaction time is as long as 20 hours, PCl3 consumption is high, equipment corrosivity is large, product purity is low, multiple times of reduced pressure distillation is needed, and a product yield is low. In CN104402709A, the TPA and the thionyl chloride are used as the raw materials, the thionyl chloride is a reactant and is also a solvent, which is hard to be completely removed by the reduced pressure distillation, and in a rectifying process, a side reaction easily happens with the TPC. An impurity is generated, and product quality is affected. In CN101935276A, a thionyl chloride synthesis method is also used, but quaternary ammonium salt is used as a catalyst, which is difficult to be recycled, and leads a solid waste amount and product cost increased. In CN10180527A, the TPA and a solid triphosgene are used as the raw materials, dichloroethane is used as a solvent, and an intermittent kettle-type reaction is executed. However, A utilization ratio of the solid triphosgene is low, a dosage of the catalyst is large, the consumption is high, and the solvent needs to be desolventized, which increases technology steps. In CN104045498, the TPA is used as the raw material without the solvent, the TPC is intermittently synthesized by a phosgenation method. However, the reaction time is several hours, and a phosgene utilization ratio is low. In JP2002020347, titanium tetrachloride is used as the catalyst, the TPC is synthesized by the phosgenation method. However, a price of the catalyst is high, and the catalyst is easily decomposed by heat and water. In U.S. Pat. No. 2,676,187, the TPA reacts with carbon tetrachloride and a chlorine gas to synthesize the TPC in 250 DEG C, a reaction temperature is high, and equipment requirements are rigorous. In U.S. Pat. No. 3,734,959, only the carbon tetrachloride is used as an acylating agent most, the reaction temperature is high, the reaction time is long, and a yield is low. In CN1072925A, paraxylene is used as the raw material, the TPC is synthesized through chlorination and hydrolysis. However, this route is long in process, complicated in technology, and a chlorination temperature is up to 200 DEG C or more, the equipment requirements are rigorous, a product yield is low, and purity is poor.
In conclusion, the TPC is synthesized mainly using a traditional kettle-type reaction as major, thionyl chloride and phosgenation methods (or triphosgene) are used. As to the thionyl chloride method, equipment is seriously corroded by recycling the raw material of the thionyl chloride. The product purity is low, and a standard may be achieved through several times of rectification under vacuum, which lead to a higher production cost. At the same time, recycling treatment of a by-product of SO2 is troublesome, and the environment may be polluted. As to the phosgene/triphosgene method, the reaction time is long, a utilization ratio of phosgene/triphosgene is low. The catalyst is easily decomposed and coked after heated for a long time, so a color of the catalyst is deep, which makes a recycling ratio of the catalyst low and the production cost higher.
So far, research of synthesizing paraphthaloyl chloride through terephthalic acid in a microchannel reactor continuous flow mode may not be seen yet. The disclosure provides a technology route of synthesizing the paraphthaloyl chloride through the terephthalic acid in the microchannel reactor continuous flow mode, the technical advantages of the route are that a reaction temperature, a feeding molar ratio and standing time can be accurately controlled, a dosage of the catalyst is low, reaction is completed within few tens of seconds to a few minutes, a utilization ratio of phosgene/triphosgene is high, production purity is high and the like.